Mimas, one of Saturn’s moons famously likened to the “Death Star” from “Star Wars” due to its distinctive Herschel Crater, harbors a secret beneath its icy, cratered exterior—a subsurface ocean. Researchers have utilized data from NASA’s Cassini spacecraft, focusing on Mimas’s rotational motion and orbit, to confirm the existence of this hidden ocean beneath an ice layer 20 to 30 kilometers thick.
This newfound ocean, believed to have formed relatively recently in cosmic terms—between 5 and 15 million years ago—positions Mimas as a point of interest for understanding the potential for life. Earth’s earliest organisms emerged in primordial seas, suggesting that liquid water is a critical component for the development of life.
Valery Lainey, an astronomer at Observatoire de Paris and the lead author of the study published in Nature, expressed surprise at the discovery, given Mimas’s outwardly inactive and heavily cratered appearance which does not immediately suggest the presence of liquid water.
Mimas now joins the ranks of other celestial bodies in our solar system, such as Saturn’s Enceladus and Titan, and Jupiter’s Europa and Ganymede, which show evidence of subsurface oceans. The presence of these oceans suggests that there could be more habitable environments within our solar system than previously thought.
The internal ocean on Mimas implies a significant heat source within the moon that transforms ice into liquid water. The moon’s elliptical orbit around Saturn subjects it to varying gravitational and tidal forces, which deform Mimas’s interior, generating heat and maintaining the water in a liquid state.
This ocean, constituting more than half of Mimas’s volume, albeit only 1.2-1.4% the volume of Earth’s oceans, presents a fascinating environment for scientific inquiry. The contact between the water and Mimas’s rocky core could potentially enable complex chemical reactions, laying the groundwork for the emergence of life.
While Enceladus has been considered a prime candidate for harboring life due to its erupting plumes and the presence of water, organic compounds, and heat, Mimas’s relatively young ocean poses questions about the timeframe necessary for life to develop. Gabriel Tobie, a planetary scientist and co-author of the study, suggests that Mimas could offer insights into the initial stages of life’s evolution, despite the challenges posed by its nascent oceanic environment.
This revelation about Mimas adds to the intrigue surrounding Saturn’s moons, furthering our understanding of the diverse and dynamic nature of celestial bodies within our solar system and their potential to support life.